1. Field of the Invention
The subject invention is related to fluid filtration devices, and more particularly, to spiral pleated filters having unique pleat configurations that develop lower pressure drops than conventional spiral pleated filters.
2. Background of the Related Art
Over the years, the design of cylindrical pleated filter cartridges has involved efforts to maximize the amount of filter media or surface area that may be fit into a filter cartridge having a given outer diameter without adversely effecting flow or filter life. In a standard radially pleated filter cartridge such as that which is disclosed in U.S. Pat. No. 3,692,184, the amount of filter media that may be packed into the cartridge is limited by the number of pleats that can be packed about the cartridge core. Consequently, there is a substantial amount of empty space between adjacent pleats at the outer periphery of the filter element.
A cylindrical filter element having a radially extending W-pleat configuration, such as that which is disclosed in U.S. Pat. No. 3,799,354 represents an improvement over a standard radially pleated filter element. The radial W-pleat configuration provides added surface area about the outer periphery of the filter element by providing relatively short pleats that extend radially inward from the outer periphery of the filter element between adjacent pleats of standard height. These shorter pleats occupy the open space near the outer periphery of the filter element. They do not, however, maximize the amount of filter media that can be disposed within the cartridge, as some empty space still remains between the pleats. The radial W-pleat construction also suffers from the effect of pleat migration, in that the shortened pleats tend to move radially inward towards the central axis of the filter. This movement is undesirable as it can cause binding, blockages, increased pressure drops across the filter, reduced filter life and can damage the filter media.
A spiral pleated filter element is comparable to a standard radially pleated filter element in that it includes a plurality of longitudinal pleats disposed in a cylindrical configuration. In a spiral pleated filter, however, the ends of the pleats are rolled over to minimize the spacing between adjacent pleat surfaces near an outer diameter of the filter element. In this case, the pleat height is substantially greater than the distance between the outer periphery of the cartridge core and the inner periphery of the cartridge cage. Consequently, in a conventional spiral pleated filter, the pleats at the outer periphery occupy the excess volume that would normally represent empty space in a radially pleated filter element.
While both the spiral pleat and the radial W-pleat designs provide increased filter surface area as compared to a standard radial pleat configuration, the spiral pleat configuration does not have the pleat migration problems associated with the radial W-pleat configuration. As compared with a radial W-pleat filter, however, the rolled-over pleats of a spiral pleated filter provide fewer and less accessible radial flow paths near the outer diameter of the filter. These factors lead to a greater pressure drop across the filter. In addition, the rolled-over pleats of a spiral pleated filter provide longer flow paths and, therefore, a greater likelihood that the flow paths will become blocked in high load or large particle contaminant applications. This condition is often referred to as bridging, and can have an adverse effect on filter life.
It has also been found that conventional spiral pleated filter elements are more difficult to insert into a cylindrical cage than standard radially pleated filter elements, because the rolled-over pleats have a tendency to straighten out prior to being inserted into the cage. As a result, the filter element can experience frictional drag along the interior surface of the cage. This can cause damage to the filter media and can, as a practical matter, limit the axial length of a filter cartridge incorporating a spiral pleated filter element.
An example of a conventional spiral pleated filter element is disclosed in U.S. Pat. No. 5,543,047 to Stoyell et al., the disclosure of which is herein incorporated by reference in its entirety. The spiral pleated filter element of Stoyell et al. comprises a three-layer composite of a filter medium, an upstream drainage layer disposed on the upstream surface of the filter medium, and a downstream drainage layer disposed on the downstream surface of the filter medium. The pleats of the filter element are dimensioned and configured in such a manner so that virtually all of the volume between the inner and outer peripheries of the filter element is occupied by the pleats. Consequently, there tends to be a high degree of pleat compaction and density at the inner periphery of the filter element, i e. at the roots of the pleats. This causes a significantly high pressure drop near the core of the filter.
In particular, the pleats of the Stoyell et al. filter element are configured such that each pleat leg abuts an adjacent pleat leg along the inner periphery of the filter element and the height of each pleat, measured in a direction along the legs and extending from the inner periphery at the root of the pleat to the outer periphery at the crown of the pleat, is greater than (Dxe2x88x92d)/2 and less than (D2xe2x88x92d2)/[4(d+2t)], where D and d are the outer diameter and inner diameter of the filter element at the outer periphery and inner periphery, respectively, and t is the thickness of each pleat leg. By dimensioning the pleats in this manner, the opposing surfaces of the pleats contact one another over substantially the entire height and axial length of the pleat legs, leaving substantially no empty space between adjacent pleats, and particularly in the region of the core. Indeed, the only space remaining at the core, are small triangular gaps that are located between adjacent pleat roots. Consequently, there is a relatively high pressure drop through the filter element.
Accordingly, there is a need in the art to provide a spiral pleated filter design that maximizes the surface area of the filter media while having a lower pressure drop across the filter element than prior art spiral pleated filter elements, and which is easier to insert into a supporting cage than prior art spiral pleated filter elements.
The subject invention is directed to a new and unique spiral pleated filter that includes a cylindrical filter element having a longitudinal axis, an outer periphery, an inner periphery and a plurality of longitudinal pleats that are disposed in close proximity to one another. Each of the pleats has a pair of legs, and each of the legs has a height. In accordance with the subject invention, the height of a first leg of a first pleat is greater than the radial distance between the outer periphery of the filter element and the inner periphery of the filter element, and is also greater than the height of an adjoining leg of an adjacent pleat.
It is envisioned that the height of the adjoining leg of the adjacent pleat ranges from about fifty percent (50%) of the height of the first leg of the first pleat to about ninety-five percent (95%) of the height of the first leg of the first pleat. Preferably, the filter element is a composite having plural layers of material including an upstream drainage layer, at least one interior filtration layer, and a downstream drainage layer. A perforated cage surrounds the outer periphery of the filter element, and a perforated core is surrounded by the inner periphery of the filter element.
It is envisioned that the pleats can be configured in several different ways. For example, the height of a second leg of the first pleat may be equal to the height of the first leg of the first pleat. Alternatively, the height of a second leg of the first pleat can be less than the height of the first leg of the first pleat, or the legs of the adjacent pleat can be equal in height. It is also envisioned that the height of a second leg of the adjacent pleat may be greater than the height of the other leg of the adjacent pleat.
The subject invention is also directed to a filter that includes a cylindrical filter element having a plurality of longitudinal pleats arranged in a spiral configuration in close proximity to one another. Each of the pleats has a pair of legs, and the legs of each pleat are joined to one another at a root. In accordance with the subject invention, the roots of adjacent pleats are radially spaced from one another about the inner periphery of the filter element. Also, the adjoining legs of adjacent pleats are connected to one another at a crest, and in an embodiment of the subject invention, the crests of adjacent pleats are radially spaced from one another about the outer periphery of the filter element.
The subject invention is also directed to a filter cartridge that includes a cylindrical filter element having a longitudinal axis, an outer periphery, an inner periphery, and a plurality of longitudinal pleats arranged in a spiral configuration in close proximity to one another. Each of the pleats has a pair of legs, and the legs of each pleat are joined to one another at a root. A perforated cage or netting surrounds the outer periphery of the filter element, and a perforated core is surrounded by the inner periphery of the filter element. In accordance with the subject invention, the roots of alternating pleats abut the perforated core. Also, adjoining legs of adjacent pleats are connected to one another at a crest, and in an embodiment of the subject invention, alternating crests abut the perforated cage.
These and other aspects of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings described hereinbelow.